The way of estimating interphase tension in the liquid aluminum alloy - liquid slag
Magdalena Suchora-Kozakiewicz, Jacek Jackowski
Quarterly No. 2, 2017 pages 73-78
DOI:
keywords: recycling, refining, interphase tensions, measurements
abstract In refining treatments (removal of solid inclusions) related to cast aluminum alloys as well as the recycling of cast metal composite material [MMK] on the matrix of aluminum and its alloys, consisting in separation of the components, substances which form another liquid phase (aside from the liquid metal (alloy)) are used. With regard to aluminum alloys, these substances are both refining fluxes and so-called recycling centers. They are composed of molten salt mixtures (mainly chlorides and fluorides). The effectiveness of their action is determined by the value of interphase tensions on the boundary with a liquid metal (alloy), which should be as small as possible. The values of interphase tensions in such system are not very well known, which led to an attempt to specify them in greater detail. A measuring station intended to specify them by means of the so-called ring test was constructed. The principle of conducting such measurements is simple but the method of their performance is difficult due to the specific properties of biphasic systems at significantly elevated temperatures. To complete the test stand (facility), a laboratory resistance crucible furnace was used and a measurement system composed of a probe that cyclically crosses the interphase boundary, the probe drive mechanism and a force gauge that continuously registers the changes in the values of forces acting on the probe. A non-standard massive cast iron crucible with a considerable thermal inertia was placed in the furnace chamber. The metal input (aluminum alloy) and salt mixtures (being refining means or recycling centers) were melted in this crucible. Trials were carried out using fixed values of the probe dimensions, speed of the probe crossing the interphase surface and frequency of registering the force gauge indications. During each series of trials, changes in the temperature values of the tested systems were recorded. It was found that both the method of measuring interphase tensions and the method of its realization performed well, ensuring reliable and reproducible results. The only drawback was the material of the probes used. The stainless steel used to make them proved to have poor resistance to the operating conditions. Despite this, the method and way of determining the interphase tension values in the systems allowed successful realization of the intended research objectives.